I have run a 15/45 combo on the street, as well as 15/48 street/track/BB, and a 15/52 at mission, ... I found 15/45 on the street really nice, would be a 15/46 for your F4i ( mine's an F4 )... the 15/48(49) is a little buzzy on the freeway...like 7500-8000rpm at 110-120kph, and the 15/52 would be up even higher....I've gone back to 15/45 for the street this year as I have bought a track bike.....the 520 chain conversion is also popular, giving you some weight savings. depending on your chain condition you may just want to slip a 15 tooth front sprocket on the chainyou have now and try it out...I think they are fairly cheap.